Ionic tube for controlling electric currents



Oct. 6, 1953 p, TOULQN 2,654,856

IONIC TUBE FOR CONTROLLING ELECTRiC CURRENTS l9 CONTROL VOLTAGE LI 1 LIB INDUCTION con. l2

as IL 3 30 2| a *7 I x I g 28 22/ V l l 23K 2| 1 27 INVENTOR c 1 I 1 E 32. u 1 Z I 29 J l/ 0 l PIERRE MARIE GABRIEL TOULON 34 5 BY a/bzagvgaim/ ATTORNEY Oct. 6, 1953 P. M. G. TOULON 72,654,356

IONIC TUBE FOR CONTROLLING ELECTRIC CURRENTS Filed Nov. 21, 1950 2 Sheets-Sheet 2 PHASE CONTROL PIERRE MARIE GABRIAL TOULON 3 INVENTOR I BY ATTORNEY Patented Oct. 6, 1953 IONIC TUBE FOR CONTROLLING ELECTRIC CURRENTS Pierre M. G. Toulon, New York, N. Y., assignor to Products and Licensing Corporation, a corporation of New York Application November 21, 1950, Serial No. 196,847 In France November 22, 1949 10 Claims.

The present invention relates generally to gaseous conduction devices, and especially to improved gaseous conduction devices capable of controlling electric currents of extremely large magnitudes.

There is presently known in the art a very large variety of gaseous conduction devices which may be employed for the control of electric current. One commonly known gaseous conduction device of this type, isthat known as the thyratron. The thyratron tube utilizes a heated cathode of the thermo-emissive type. For that reason, tubes of the thyratron type have very definite upper limits to the magnitude of the discharge currents they are able to handle. When these limits are exceeded the cathodes of the tubes deteriorate rapidly.

Another well known type of gaseous conduction device is the ignitron, which utilizes a cold liquid cathode, on the surface of which may be made to appear, at controlled instants of time, a conductive spot, by utilizing a special electrode known as an ignitor. This electrode generally consists of a rod of semi-conducting material, such as carborundum, which dips into the liquid cathode, generally a mercury pool. By passing a current from this rod to the mercury, minute areas form at the point of contact between the rod and the mercury, facilitating the formation of the main are between the anode and the oathode. The firing of an ignitron requires the eX- penditure of a definite and rather large amount of energy, in contrast to the thyratron, where -firing is essentially a matter of electro-static The current flow required to fire the control. ignitron tube may be of the order of 30 amperes or more, but this disadvantage is made up for by the high current carrying capacity and overload capacity that the ignitron possesses. A

.further disadvantage which the ignitron tube possesses is that the ignitor electrode is relative- 1y fragile, and tends to deteriorate rapidly. The fact that the firing of ignitrons requires currents of the order of 30 amperes involves considerable practical difiiculty and cost, in providing the necessary control circuits and devices. It is usual at the present time to provide a thyratron control circuit for supplying current to the ignitor electrode, and to control the firing times of the thyratron in order to control the firing It is nevertheless true that the mercury pool type of tube is basically suitable for carrying and controlling extremely large currents. Accordingly, considerable attention has been devoted in the art to methods of causing ignition of such tubes and of controlling the firing times thereof. It is a primary object of the present invention to provide a novel and simplified gas eous conduction device utilizing a mercury pool cathode.

It is a further object of the invention to provide a gaseous conduction device utilizing a mercury pool cathode, the firing of which. may be controlled by means of a control electrode which draws substantially no current, in comparison with the intensity of the current controlled by the tube.

It is a further object of the invention to provide a gaseous conduction device, having a mercury pool cathode in which no movable parts are employed for initiating conduction in the device.

Still another object of the invention resides in the provision of novel cooling structure for a tube of the character here involved.

A further object of the present invention resides in the provision of a gaseous conduction device having a mercury pool cathode, in which there is maintained in a portion of the tube a permanently ionized gaseous plasma, isolated by a negatively polarized control electrode, the ionization spreading to the remainder of the tube when the control electrode is made positive, or equal in potential to the cathode, thereby enabling conduction between the anode and cathode of the tube.

Still further, it is an object of the present invention to provide a complete system of rectification, utilizing the gaseous conduction devices of the invention, and supplying D.-C. voltage and current from a three phase line.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of an embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

Figure l is a longitudinal cross-section through a tube constructed in accordance with the present invention, together with an illustration of various fundamental electrical controls for the tube.

Figure 2 is a view in longitudinal section of cooling structure applied to the tube of Figure l, the latter being shown in elevation; and,

Figure 3 is a schematic circuit diagram of a rectifier operating from a three phase source, and utilizing gaseous conduction devices in accordance with the present invention.

Briefly described, in accordance with the present invention, a cathodic spot is obtained in a mercury pool type gaseous conduction device, by filling the tube With a low pressure gas such as helium or xenon. The presence of this gas in the tube permits generation of a spark on the surface of the mercury when high tension is applied between a first auxiliary electrode and the cathode. Such high tension may readily be applied by means of an induction coil, and it is found that extremely low values of current are sufficient to cause generation of such spark. A further auxiliary electrode is provided, to which is applied a D.-C. steady voltage, and which picks up and maintains the cathodic spot, in response to the continuous flow of one of two amperes of current.

A control electrode in the form of a grid is superposed over the mercury pool, and interposed between the mercury pool and an anode. The control electrode is maintained normally at a negative potential. When so maintained a gaseous plasma forms in the volume of the tube intermediate the cathode and the control electrode, and is restricted to that volume by the negative control electrode.

In order to effect current flow between the anode and cathode, the potential of the control electrode may be raised to that of the cathode or above, while the anode is positive. Current flow to the anode will then be initiated, and the control electrode will lose control of the magnitude of this current, and be unable to terminate it. The current flow will continue until the voltage of the anode falls to zero or becomes negative.

Accordingly, control of the relative phases of the voltages applied to the anode and the control electrode of the tube is sufficient to control the magnitude of current flow through the tube, as is the case in thyratron and ignitron technique. At the same time, a relatively small steady current is sufficient to maintain the tube in condition to be rendered conductive in response to a very small grid current.

Accordingly, my novel tube possesses the advantage of an ignitron, in that it passes currents of the same magnitude as are passed by ignitrons, and also the advantages of the thyratron type tube, in that very small grid currents are required to control anode current flow.

In a preferred construction utilizing the principles of my improved tube, the container for the tube elements may be fabricated of glass, and all the controlled elements including the cathode lead may be arranged in the base of the tube, no leads or control elements extending through the sides of the tube, which may be arranged cylindrically, and the anode extending vertically downward through the upper wall of the tube. This construction materially simplifies problems of cooling the tube, since a cooling jacket may be clamped about the cylindrical wall of the tube without interfering with any of the leads or seals.

Utilizing a plurality of tubes, constructed in accordance with the invention, for purposes of rectification, a single induction coil may be utilized to produce sparks for initiating ionization in all of the tubes, and the output of the induction coil being at a relatively high frequency, may be applied to the sparking electrodes through condensers, which then serve as isolating means for low frequency currents.

Those electrodes which provide D.-C. currents to the tubes may be fed from relatively small rectifiers, which may be of the copper oxide type,

for example, and which are supplied with A.-C. from the power leads.

Referring now more specifically to the drawings, the reference numeral l identifies the envelope of the gaseous conduction device arranged in accordance with the invention, and thi envelope may preferably be fabricated of glass of a suitable type. I do not, however, exclude the possibility that the envelope may be fabricated of metal, a is the common practice in the case of ignitrons. However, such an arrangement will necessitate structural modifications of the tube, which, it is believed, will be obvious to those skilled in the art, from the description of the invention as embodied in a tube having a glass envelope. A relatively large anode 2 may be provided, which may be fabricated of graphite, and the size of which may be determined primarily by the magnitude of the current which it must carry. The anode 2 may be supported by an output lead 3 of considerable cross section, which extends through the cap of the envelope 1, by means of a seal. Sealing techniques are well known per se, and accordingly, I shall not disclose or describe the details thereof.

A cathode, in the form of a pool of mercury 4, is located in the lowermost portion of the envelope l, and is connected to points externally of the envelope I by means of a lead 5, suitably sealed to the envelope and extending to within the mercury pool through the base of the envelope I.

A first auxiliary electrode 6 is provided, which passes upwardly through the base of the envelope l and through the mercury pool 4, at a point displaced from the axis of the tube, proceeding then parallel to the surface of the mercury tube, and to a point axially of the tube and displaced but a slight distance from the surface of the mercury. The electrode 6 is encased in a glass envelope 1 for most of its length, in order to provide insulation with respect to the mercury pool 4, and in order, further, that a high tension spark may be applied to the lead 6 for application only to the surface of the mercury along the axis of the tube.

The tube is filled with a low pressure nonliquefiable gas, which is not absorbed by the electrodes or by the mercury, and which may be helium or xenon, at a pressure of the order of a millimeter of mercury. As a consequence of the presence of this gas, if a sufficiently high voltage is applied between the electrode 6 and the mercury pool 4, as by means of an induction coil 8, a spark appears on the mercury surface.

A further auxiliary electrode 9 is provided, which is supplied with electrical power by means of a lead H), which passes through the mercury pool 4 in a glass envelope H, as in the case of the electrode 6. The electrode 9 is supplied with positive D.-C. voltage from a source of such voltage, conventionally illustrated as a battery l2.

From the spark generated by the electrode 6 in response to voltage supplied by induction coil 8, there is generated a cathode spot, when the electrode 9 is positive. Travel of this cathodic spot to any considerable extent with respect to the longitudinal axis of the envelope I is prevented by means of a ring l3, of conductive material, supported as by glass supports l4, and which provides an isolating means for the spot.

A control electrode IS, in the form of a grid, which may be fabricated of graphite, extends transversely of the longitudinal axis of the tube,

and efiectively separates the envelope I into two parts, one subsisting below the grid I5 and the other above the grid I5, while the grid I5 is maintained at a negative potential with respect to the cathode 4. Such negative potential is maintained by means of a negative voltage source conventionally illustrated as a battery IE. The grid structure I5, when maintained at negative polarization, prevents ionized plasma from reaching the anode 2, so that the tube remains non-conductive even if a positive voltage is applied between the anode 2 and the oathode 4. If, however, while part of the potential is applied to the anode 2, the grid I5 is brought to the same voltage as the cathode, or approximately the same voltage, or slightly more positive than that voltage, current flow commences between the cathode and anode. The control electrode immediately loses control of current flow to the anode, and such current flow may then be terminated only by reducing the voltage of the anode to zero, or approximately to zero, or by making the anode negative with respect to the cathode.

It will be seen then that the tube operates substantially in the manner of a thyratron. However, because it utilizes a mercury pool cathode, it is capable of controlling and handling currents of the order of magnitude of those controlled and handled by ignitron tubes or mercury arc rectifiers.

The grid I5 may be supported by a glass column, I6, through which extends a grid lead H, to a point externally of the envelope I, so that the latter may be supplied with negative voltage by the battery I6, and with an alternating current control voltage supplied from a source I8. A further source of alternating current voltage I9 may be controlled between the cathode lead 5 and the anode lead 3, whereupon D.-C. voltage will appear at the terminals 29, when a suitable load is connected therebetween.

It will be noted that none of the electrodes of the device embodying the present invention need be moved, but that on the contrary all the parts are fixed. This is in direct contra-distinction to the practice in the case of known mercury rectifiers.

It will be further clear that, except for the anode, all the electrode structure is supported by the base of the tube, enabling a very clean and economical structure.

A further point may be noted, that relatively small power is required to maintain the tube in firing condition. I have further found that the stability of the cathodic spot is unusually excellent in the present device, because the current flow from the electrode 9 is constant, and may be adjusted to have always an optimum value for cathodic spot maintenance.

Reference is now made to Figure 2 of the accompanying drawings wherein is illustrated the structure utilized for cooling the envelope I dur ing its operation. Since the internal structure of the device is of relatively slight importance in discussing the cooling arangement, the internal structure is not illustrated in Figure 2, but the envelope i is shown in plan, together with the anode lead 3 and the cathode lead 5.

Considering the lateral wall of the envelope as a cylinder, there is provided for the upper and lower edges of this cylinder rubber rings 2I, which are of trapezoidal cross section. The inner wall of each ring 2| rests on an extremity of the cylindrical wall of the envelope I, while the outer walls of the rings 2I bear against suitably shaped upper and lower edges of an encasing cylinder 22, which may preferably be fabricated of glass in order to enable examination of the interior of the glass envelope I, and examination of the operation of the tube and of the nature of the arcs formed. I prefer, however, to utilize a metallic cylinder, in order to provide superior mechanical protection to the envelope I, which is itself made of glass.

The cylindrical shell 22 may be provided with a water inlet 23 and a water outlet 24, provided with detachable feed pipes, which may be flexible in order to avoid transmission of shocks to the casing.

Interiorly of the cylindrical wall casing 22 is a spiral water guard 25, which forces the water to ascend in a spiral path upwardly from its inlet at 23 to its outlet at 24, the water being during all this time in direct contact with the envelope I, thereby serving to cool the latter.

In order to render the structure water tight, it is necessary merely to exert pressure on the rings 2I, tending to force these together, thereby exerting a wedging action as between the envelope I and the upper and lower portions of the casing 22. To this end there are provided upper and lower metallic rings, the upper ring being 26 and the lower ring 21, and these rings bearing against the rubber rings 2I, respectively and being forced together by means of draw bolts 28, one end of each of which may for example, be hingedly secured to the lower metal ring 21, and the other end of which may be tightened by means of a ring nut 30.

Cylindrical supports, as 3|, may be welded to the lower metallic ring 21, and these may be provided with pedestals, as 32, having apertures through which may be passed suitable screw fastening means, as 33, in order to bolt the entire structure to a rigid support, as 34.

Havin reference now to Figure 3 of the accompanying drawings, there is shown a'three phase power source 31, from which is to be derived by a process of full wave rectification, a D.-C. voltage. In order to accomplish such rectiflcation there is employed six tubes of the gaseous conduction type, arranged in accordance with the present invention, these tubes being identified respectively by the numerals 38 to 43, inclusive. The anodes of the tubes 38, 39 and 48 are connected each to a different phase of the three phase line 31, and the cathode of the tube 4| is connected to the anode of the tube 38, the cathode of the tube 42 to the anode of the tube 39, and the cathode of the tube 43 to the anode of the tube 40. The tubes are accordingly connected in back-to-back relation by pairs, or in inverse parallel relation across each phase of the three phase source 31. The cathodes of the tubes 38, 39 and 4|] may be connected together and to the positive output terminal, while the anodes of the tubes 4|, 42 and 43 may likewise be connected and to the negative termi-- nal of the output leads, the latter being identified by the reference numeral 44.

The general arrangement of six gaseous conduction devices in conjunction with a three phase line, to accomplish rectification, is per se old. The novelty of the arrangement resides in the provision of my novel tubes in the circuit, and in the manner in which I control the tubes from thethree phase line.

In order to supply D.-C. voltage to the auxiliary anodes which maintain the cathode spots in the tubes 38 to 43, inclusive, there is provided a transformer 45, having, a primary winding 4e, and six secondary windings, 41 to 53, inclusive, each of which is center-tapped and each of which supplies 1).-C. voltage and current of approxite y one or two amperes to the appropriate electrodes of the tubes 38 to 43, inclusive.

Each of the secondary windings 41 to 52, inclusive, is connected. in a conventional full wave rectifier circuit, comprising a pair of dry rectifiers, as 54,. 55 connected. in the secondary 41, and similar dry rectifiers in the remaining ones of the secondaries. 43 to 46, inclusive. The centor-tap of each of the windings 41 to 52, inclusive, then becomes a negative terminal of the rectifier, and the cathodes of the dry rectifiers are. connected respectively to positive supply leads, as 56, 51, 58, 59-, B9. and El, respectively. Between each of leads 56 to El, inclusive, and the center-tap of the corresponding secondary winding 4'! to 52, inclusive, is connected a smoothing condenser, as 62 to. 61 inclusive, in the case of the secondary windings 4! to 52, inclusive. Additionally, there is connected in series with each of the leads. 5%, 81, inclusive, resistances, as '68 to E3, respectively, which serve to limit current flow in the leads 56 to 53, respectively. The leads 56 to 6! respectively, are connected with the D.-C. auxiliary electrodes of the tubes 38 to 43, respectively, and supply these with the necessary D.-C. voltages and currents.

In order to initiate formation of a cathode spot in each of the tubes 38 to 43, and thereby to form gaseous plasma below the control electrodes of the tubes 38 to 43, respectively, there is provided a secondary winding 53 for the transformer 45, and which supplies alternating current to a rectifier unit '15, of the Rectox type, the latter having across its D.-C. terminals a storage condenser, as 15, and a primary winding is supplied with a maker and breaker points ll, which, when bridged by an armature '18, close the circuit to the winding I6, and which, when open, provide an open circuit in series with the Winding Hi.

When the winding 15 is energized it pulls up on the armature 18, breaking its own circuit, whereupon the armature 18 falls again completing the circuit to the winding '56. This alternate make and break continues so long as voltage is available across the condenser 15.

The repeated making and breaking of the circuit of the primary winding it results in the induction of high voltage in the secondary winding 19, inductively coupled to the primary winding 16. One terminal of the secondary winding 75 is connected to the selector arm Bl of a selector switch 82, having six contacts 33 to 88, inclusive, which lead to the spark forming auxiliary electrodes of the tubes 38 to 43, respectively. Accordingly, any selected one of the spark forming auxiliary electrodes may be connected in circuit with secondary winding it, by suitable manipulation of the rotary selector arm 8|.

Connected in parallel to the remaining terminal of the secondary winding is are four condensers $9 to $32, inclusive, the condenser 89 leading in parallel to the cathodes of all the tubes 38, 39 and 4B, the condenser 90 leading to the cathode of the tube 4|, the condenser 9| to the cathode of the tube 42 and the condenser 92 to the cathode of the tube 43. The signal generated by the secondary winding is at relatively high frequency, since it is caused by the rapid make and break of an inductive circuit, as is well. known in the art, and the. condensers 8,9 to 92, inclusive, constitute a very low impedance to this high frequency current, Looked at in another way, the wave front of the voltage supplied by the secondary winding H is very steep, corresponding with high frequency components, and this steep wave front passes through the condensers 89 to 92, as if they were of low impedance. Accordingly, any one of the tubes 38 to 43, inclusive, may have a. high frequency voltage impulse applied to its spark forming auxiliary electrode, by suitably positioning the selector arm 8i. In operation the selector arm 8| may be rotated to bring it into contact with the contacts 83 to 88, inclusive, in succession, thus forming a spark on the surface of the mercury cathodes of the tubes 38 to 43, respectively, in sequence. When a spark is formed at any one of these cathodes appropriate D.-C. voltage is available on the leads 5% to 60, inclusive, to form a cathode spot by virtue of. the operation of the 1).-C. auxiliary electrodes of the tubes, (corresponding in each case with the electrode 9 in the case of the tube of Figure 1). There. is thus established a gaseous ionized plasma in each or the tubes, 38-43, inclusive.

1).-C. operating voltages are supplied to the control. eiectrodes of the tubes 38 to 23, inclusive, via a phase control device, generally indicated by the reference niuneral 39., and supplied with operating voltages via the. leads to supplied from the three phase line 3?. The phase control device 85 may be of known type, and provides voltage output of controllable phase, to enable control of the firing times of the tubes 33 to 43, and thereby the voltage output available at the terriinals While I have described and. illustrated specific forms of the invention it will be clear that variations thereof may be resorted to without departing from the true scope of the invention as defined in the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

l. The combination of at least one pair of rectifiers, each of rectifiers comprising a mercury pool cathode, an anode, a control grid, a first control electrode and a second control electrode, said second electrode physically separated from said cathode, a single induction coil for supplying voltage pulses of steep wave front to second electrode of each of said rectifiers to initiate a spark at each of said cathodes, and means for supplying continuous direct voltage separately between each of said first electrodes and its mercury pool cathode to maintain an. arc therebetween.

2. The combination of at least one pair of inverse parallel connected rectifiers, a source of alternating voltage connected across said rectifiers, each of said rectifiers comprising a mercury pool cathode, an anode, a control and a first and second control electrode, an induction coil having a periodically interrupted primary winding and a secondary winding, means for energiz ing said primary winding from said source of alternating voltage, plurality of condensers for coupling said secondary winding to a first control electrode of each of said parallel connected rectifiers, said condensers presenting each a high impedance at. the frequency of said alternating voltage, and a low impedance to the output of said secondary winding.

3. In a three phase to D.-C. rectifier system, a three phase line, six gaseous conduction de- 9 vices, each having an anode, a cathode of the liquid type, an electrostatic control electrode, an arc maintaining electrode, and a spark forming electrode, said electrodes all hysically separated from said cathode, means connecting each of three of said anodes to a separate phase of said three phase line, and the cathodes of the corresponding gaseous conduction devices to a common positive line, means connecting each of the cathodes of the remaining gaseous conduction devices to a separate phase of said three phase line, and the anodes of the corresponding gaseous conduction devices to a common negative line, a separate rectifier for supplying direct current between each of said are maintaining electrodes and the corresponding cathode, a single induction coil of the vibrating armature type for generating pulses of steep wave front, said conduction coil comprisin an output winding, means for selectively connecting one terminal of said output winding to said spark forming electrodes, one by one, separate condensers connected each between the remaining terminal of said output winding and one of said cathodes of the remaining gaseous conduction devices, and a further condenser connected between said remaining terminal of said output winding and the cathodes of said corresponding gaseous conduction devices, each of said condensers having relatively low impedance to said pulses of steep wave front, and relatively high impedance to currents supplied by said three phase line.

l. In combination, for rectifying current supplied by a two wire A.C. line to a two terminal load, a first gaseous conduction device having a first anode connected to one of the lines of said two wire A.-C. line and a first liquid cathode connected to one terminal of said load, a second gaseous conduction device having a second anode connected to the other terminal of said load and a second liquid cathode connected to the other line of said two wire A.-C. line, said first device comprising a first holding electrode, a first sparking electrode and a first electrostatic control electrode all physically separated from said first cathode, said second device comprising a second holding electrode, a second sparking electrode and a second electrostatic control electrode all physically separated from said second cathode, a first source of positive direct current of predetermined amplitude connected between said first holding electrode and said first cathode, a second source of positive direct current of predetermined amplitude connected between said second holding electrode and said second cathode, a single source of high frequency sparking voltage, means for applying said sparking voltage selectively between said first sparking electrc-de and first cathode, and said second sparkin electrode and second cathode, and condenser means for isolating said sparking electrodes from said holding electrodes for direct current and for the frequency of said A.-C. line.

5. The combination of a gaseous conduction device comprising a container having therein an anode, a liquid cathode, a sparking electrode physically separated from said liquid cathode, an are holding electrode physically separated from said liquid cathode, and an electrostatic control electrode for controlling transfer of ourrent between said anode and said liquid cathode,

an isolating condenser for coupling said source of high frequency current between said sparking electrode and said cathode, said isolating condenser having a low impedance to said high frequency current, and means for applying voltages of relatively controllable phase between said anode and cathode and between said electrostatic control electrode and cathode.

6. The combination in accordance with claim 5 wherein said gaseous conduction device is connected in series between an A.-C. line of predetermined frequency and a load, and wherein said isolating condenser possesses high impedance at said predetermined frequency.

7. In a system for transferring current from a multi-phase line of predetermined frequency to a load, a separate gaseous conduction device connected between each phase of said multi-phase line and said load, said gaseous conduction devices each comprising an anode connected to a phase of said multi-phase line and a cathode, all said cathodes connected together by a path of substantially zero impedance, each of said gaseou conduction devices comprising further an electrostatic control electrode, an are holding electrode and a sparking electrode physically separated from its cathode, a separate source of positive direct current connected between each of said are holding electrodes and said cathodes, a single source of high frequency voltage, means for applying said high frequency voltage in sequence between said sparking electrodes and said cathodes, said last means comprising at least one isolating condenser for isolating said sparking electrodes from said cathodes for direct current and for current of said predetermined frequency, said at least one isolating condenser having low impedance at said high frequency.

8. The system of claim 7 in which said separate source of positive direct current comprises a transformer having a primary Winding coupled to one phase of said multi-phase line and having a plurality of center-tapped secondary windings, the ends of each of said center-tapped secondaries being coupled through rectifiers to said are holding electrodes and said center-taps being coupled to said cathodes.

9. The system of claim 8 in which said source of high frequency voltage comprises a further secondary winding on said transformer, rectifying means coupling said further secondary winding to an induction coil, and a vibrator-interrupter in series with said induction coil.

10. The system of claim 9 in which said source of high frequency voltage further includes an output coil magnetically coupled to said induction coil, said isolating condenser being coupled between at least one of said cathodes and one end of said output coil, said means for applying said high frequency voltage in sequence comprising switching means coupled between said sparking electrodes and the other end of said output coil.

PIERRE M. G. TOULON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,128,862 Tonks Aug. 30, 1938 2,182,633 Klemperer Dec. 5, 1939 2,354,031 La. Forge July 18, 1944 2,424,104 Lord July 15, 1947 2,428,543 Boyer Oct. 7, 1947 2,566,843 Garbuny Q- Apr. 12, 1949 

